SinkholeOdds

Sinkhole risk in Oglala Lakota County, SD: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock
4%
At or near the surface
4%
Buried under cover
0%

The next step for one property

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 73 of Oglala Lakota County's 2,094 square miles on soluble rock, 73 of them with the rock at or near the surface. With about 13,360 residents (6 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 368 map points about 2.4 miles apart, so a pocket smaller than that can be missed or overstated.

Read next: why gypsum and salt move faster than limestone, and how these percentages are measured.

Counties around Oglala Lakota County

The nearest county rated sinkhole country is Fall River County, SD, about 48 miles west. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

What Oglala Lakota County is built on

The largest mapped soluble unit here is the Niobrara Formation (limestone), Late Cretaceous in age, covering about 2% of the county. Next is the Pierre Shale at 2%.

2% of the county sits on gypsum or salt, which dissolves in years rather than millennia. That share matters more than its size suggests.

Against the rest of South Dakota

Oglala Lakota County ranks 7 of 66 in South Dakota for soluble rock at the surface, and sits above 61% of US counties on that measure.